The interaction of HeII with a solid oscillating (20,34 and 48 MHz) boundary has been studied between 0.03K and T[lambda] by an experimental technique based on the measurements of the change in resonant frequency and Q factor of a shear-mode quartz crystal immersed in the liquid. The results show three separate aspects of this interaction. (i) Below 0.6K the measurements indicate a non-viscous mechanism which is attributed to the formation of a solid layer of 4He atoms on the crystal surface. Estimates of the total adsorbed areal density reveal it to be a monolayer, characterised by a thermal mobilisation energy of 0.15K. (ii) Measurements in the middle temperature region (0.6 T T[lambda]) are used to determine the (complex) transverse acoustic impedance and hence the effective viscosity of Hell. The data is at sufficiently high frequencies to observe the breakdown in hydrodynamics which occurs when the viscous wave penetration depth [delta] becomes comparable to the phonon and roton mean free paths. (iii) Very precise measurements of the change in Q factor near T[lambda] show that the viscous wave samples an enhanced normal fluid density next to the crystal surface when [delta] becomes smaller than [xi], the superfluid healing length. A simple model is developed for the viscous losses in this region which enables an estimate to be made of the amplitude and temperature dependence of [xi]. The results are found to be well described by a power law [xi] = [xi] = [xi]0 (1 - T/T[lambda])-2/3 where [xi]0 = 0.08 nm. The transverse acoustic impedance of a weakly interacting Fermi-liquid is derived from an exact solution of the Landau kinetic equation. Explicit computations for a Fermi-gas are presented.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:704609 |
| Date | January 1983 |
| Creators | Retz, Patrick William |
| Publisher | Royal Holloway, University of London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://repository.royalholloway.ac.uk/items/f19f94ef-fd2a-4606-b015-05e9806d5974/1/ |
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